Coffee brewers where the user is able to select the volume of water used for brewing have become very popular in the past ten years. Many of these coffee brewers utilize a pre-packaged coffee pod, cartridge or capsule. Pre-packaged coffee pods, cartridges or capsules include a measured portion of ground coffee packaged in a structure that constrains the coffee while permitting hot water to flow through for extraction of flavor and aroma from the ground coffee.
It has become a prerequisite in brewing a cup at a time that the brew cycle remains short, preferably between 30 and 60 seconds and, during which time up to 300 milliliters of hot water must be channeled through the coffee pods, cartridges or capsules, and pass through a dense bed of coffee grounds. This results in a high flow rate that creates a high hydraulic resistance to the flow of water through the coffee pods, cartridges or capsules and the grounds therein. Therefore, the water has to be delivered to the coffee pod or capsule under an elevated pressure to be able to flow through the coffee pods, cartridges or capsules in a short amount of time. It has also become a prerequisite in brewing a cup at a time to use varying amounts of water according to the drinking habits of the user (some like to use small amounts of water resulting in an extra strong cup of coffee, others like their coffee diluted, thereby using larger volume of water). It is also a prerequisite that the volume of water delivered remains within a close tolerance of what is selected by the user. Another prerequisite in brewing a cup at a time is the desire to minimize the wait between each brewing cycle,
Brewing under pressure requires that the coffee brewing appliance contain a pump for elevating the water pressure to permit it to flow during the short brewing cycle through the dense coffee pod or capsule, as mentioned above. Typically electromagnetic pumps are being used in most such coffee brewing appliances. These pumps generate the water pressure needed by incorporating a reciprocating steel core that is activated by an electromagnetic field generated through an electric coil surrounding the core. There are many such pump designs, one typical such pump is described in U.S. Pat. No. 4,389,169. The typical electromagnetic pump for use in such coffee brewing appliances delivers about 600 ml per minute (Approximately 20 fl. oz. per minute), while developing a head of approximately 1 atmosphere (Approximately 14-15 PSI). This type of pump requires very tight manufacturing tolerances and high quality materials and is therefore expensive in relationship to the rest of the coffee brewer parts. Typically such pumps cost $4.00 to $6.00, even when purchased in very large quantities. Electromagnetic pumps are also known to generate a loud vibration sound.
Because of the cost and noise issues designers of single serve coffee brewers have attempted to come up with alternative designs to eliminate the use of such a pump in coffee brewers, in a number of ways, for example:
U.S. patent application Ser. No. 11/123,038 discloses a brewer incorporating a water heater, which can be hermetically sealed after filling it with water. In such a water heater water is heated to a temperature which corresponds with the pressure of 1 atmosphere above room pressure in order to use that pressure to drive the heated water through the dense pod for extracting the coffee flavor and aroma. Unfortunately, to elevate the water pressure by one atmosphere the water has to be heated to a temperature of about 120° Centigrade, which is too high a temperature for brewing coffee. The coffee brewed at that temperature is bitter and lacks aroma. Ideally, coffee should be brewed at about 92 Centigrade.
U.S. Pat. No. 8,180,204 discloses a design that uses a sealed water heater divided into two compartments one containing hot water the other containing water at room temperature and means for mixing water as it exits the water heater to maintain a resultant temperature of about 92 C.
U.S. Pat. Nos. 3,371,592, 6,082,247, 6,142,063, 6,666,130, 7,398,726, 7,640,845, and U.S. patent applications Ser. Nos. 11/393,615, 11/055,411, and 11/548,676 disclose coffee brewers that utilize an air pump that pressurizes the water container and causes the water to be delivered under pressure into the brew chamber containing the pod, cartridge or capsule. The coffee brewers described in these patents tend to be very complicated and subsequently would be expensive to produce, because of the large number of components used in the apparatus described in the patents listed here. These coffee brewers would also tend to be large to contain all the components, and will require a lot kitchen counter space. Also, owing to their large size these coffee brewers would be expensive to ship from their manufacturing venue (primarily China) to the market (primarily North America).
U.S. patent applications Ser. Nos. 11/899,952, 11/899,966, and 11/899,956 disclose a relatively compact single serve coffee brewer employing an air pump to pressurize the water heater for delivering water to the brew chamber. However the brewers disclosed do not include a cold water tank, requiring that the user refills the brewer with water before the brewer is to be used. Resulting in a long wait for the water to heat up, and the inconvenience associated with the need to refill water before each brewing cycle.
Most coffee brewers for brewing a cup at a time include flow meters through which the water flows to determine at all times the volume of water being delivered for infusion. Typically such flow meters are known as “turbine flow meters” as they incorporate a free spinning bladed wheel upon which water is injected to cause such wheel to turn in response to the velocity of water. A magnet is embedded in the hub of the wheel and a magnetic pick up exterior to the flow meter housing relays the number of turns to the control circuit. U.S. Pat. No. 8,375,845 as well as publications 20050160918, 20110281000, and 20120121769 make reference to such flow meters being used in hot beverage brewers. A flow meter that is frequently used in hot beverage brewers is Model No PVDF flow meter distributed by Daitron (www.daitron.com)
Reference is also made to pending, co-invented, and co-owned U.S. Utility patent application Ser. No. 13/297,625, the teachings of which are incorporated herein in their entirety by reference.